4 ms·

No mention of all the bedrock underneath Manhattan? Really? EDIT: specifically metamorphic bedrock

by fastball 6y ago

vidanay 6y ago
I'm pretty sure there's bedrock in the rest of the world that gets tunneled through. It's not unique to Manhattan.
- lbriner 6y ago
  Sure, bedrock would slow a project down but it wouldn't explain the higher level of labour. If you are moving more slowly, you need less people to keep the supply chain moving, not more. I saw a TV show with a standard Tunnel Boring Machine and it was about 5 men operating it (plus the automated materials feed). Even if they were paid $1M a year, it would still be loads cheaper than these tunnels are costing New York.
- fastball 6y ago
  As far as I'm aware, it actually kinda is (at least compared to other major cities with lots of tunneling). London for instance is built on sedimentary rock (mostly limestone?). The metamorphic bedrock (mostly mica?) Manhattan is on top of is obviously much harder than that.
  - vidanay 6y ago
    If you are referring to the actual Manhattan Schist type of rock, then yes that can have an effect on the cost of tunneling, but that wasn't really what your original post said - you just said "all the bedrock". Switzerland recently completed the Gotthard Base tunnel which is almost all hard rock mining.
    - fastball 6y ago
      I'm no geologist, but I was under the impression that "bedrock" generally refers to this harder type of rock. It is not just a word for any rock that things are built on. Maybe I'm wrong though. I've never heard London referred to as being built on top of bedrock in the same way I've heard it of NYC.
      - vidanay 6y ago
        Bedrock is a generic term for the hard(er) layer of rock underneath the softer stuff. Manhattan has very tough bedrock (schist) London has very soft bedrock (chalk and London Clay) - and it's also deeper
mannykannot 6y ago
That is a resasonable question, but I think it would have been mentioned if it is a significant issue. Tunnelling through the Alps is also bedrock tunnelling, and not near-surface bedrock, either. The Gothard Base Tunnel, completed in 2016, cost $12 bn and is 35.5 miles long [1]. The London Crossrail tunnels are not in bedrock, but there was some significant engineering in threading around and between existing infrastructure, and in protecting it. For all I know, bedrock tunnelling may be easier. [1] https://www.latimes.com/world/la-fg-switzerland-rail-tunnel-20160601-snap-story.html https://www.latimes.com/world/la-fg-switzerland-rail-tunnel-...
- fastball 6y ago
  Presumably tunneling through a mountain is much easier than underground because either end is just open. Very easy to get your boring machine into position / service it when needed (by just pulling it back out into the open air). Also probably less issues with damp, etc.
  - mauvehaus 6y ago
    Tunnel boring machines (TBMs) bore a gross diameter hole that's then lined (often with concrete segments) for support. The net diameter of the hole behind the TBM is less than the diameter of the TBM, particularly the shield, which is the business end. Maintenance is done in place. Fun Chunnel fact: when the TBMs driving from England and France met, they drove one below the other and abandoned it in place. The other was dismantled and removed in pieces.
jcranmer 6y ago
The geologic nature of Manhattan probably adds a small amount of cost premium to Manhattan versus more geological uniform countries. However, bedrock isn't the hardest thing to tunnel through I believe (I think it's soft-soil landfill, since the ground has far less inherent rigidity).

No mention of all the bedrock underneath Manhattan? Really? EDIT: specifically metamorphic bedrock

vidanay 6y ago

I'm pretty sure there's bedrock in the rest of the world that gets tunneled through. It's not unique to Manhattan.

lbriner 6y ago
Sure, bedrock would slow a project down but it wouldn't explain the higher level of labour. If you are moving more slowly, you need less people to keep the supply chain moving, not more. I saw a TV show with a standard Tunnel Boring Machine and it was about 5 men operating it (plus the automated materials feed). Even if they were paid $1M a year, it would still be loads cheaper than these tunnels are costing New York.
fastball 6y ago
As far as I'm aware, it actually kinda is (at least compared to other major cities with lots of tunneling). London for instance is built on sedimentary rock (mostly limestone?). The metamorphic bedrock (mostly mica?) Manhattan is on top of is obviously much harder than that.
- vidanay 6y ago
  If you are referring to the actual Manhattan Schist type of rock, then yes that can have an effect on the cost of tunneling, but that wasn't really what your original post said - you just said "all the bedrock". Switzerland recently completed the Gotthard Base tunnel which is almost all hard rock mining.
  - fastball 6y ago
    I'm no geologist, but I was under the impression that "bedrock" generally refers to this harder type of rock. It is not just a word for any rock that things are built on. Maybe I'm wrong though. I've never heard London referred to as being built on top of bedrock in the same way I've heard it of NYC.
    - vidanay 6y ago
      Bedrock is a generic term for the hard(er) layer of rock underneath the softer stuff. Manhattan has very tough bedrock (schist) London has very soft bedrock (chalk and London Clay) - and it's also deeper

mannykannot 6y ago

That is a resasonable question, but I think it would have been mentioned if it is a significant issue. Tunnelling through the Alps is also bedrock tunnelling, and not near-surface bedrock, either. The Gothard Base Tunnel, completed in 2016, cost $12 bn and is 35.5 miles long [1]. The London Crossrail tunnels are not in bedrock, but there was some significant engineering in threading around and between existing infrastructure, and in protecting it. For all I know, bedrock tunnelling may be easier. [1] https://www.latimes.com/world/la-fg-switzerland-rail-tunnel-20160601-snap-story.html https://www.latimes.com/world/la-fg-switzerland-rail-tunnel-...

fastball 6y ago
Presumably tunneling through a mountain is much easier than underground because either end is just open. Very easy to get your boring machine into position / service it when needed (by just pulling it back out into the open air). Also probably less issues with damp, etc.
- mauvehaus 6y ago
  Tunnel boring machines (TBMs) bore a gross diameter hole that's then lined (often with concrete segments) for support. The net diameter of the hole behind the TBM is less than the diameter of the TBM, particularly the shield, which is the business end. Maintenance is done in place. Fun Chunnel fact: when the TBMs driving from England and France met, they drove one below the other and abandoned it in place. The other was dismantled and removed in pieces.

jcranmer 6y ago

The geologic nature of Manhattan probably adds a small amount of cost premium to Manhattan versus more geological uniform countries. However, bedrock isn't the hardest thing to tunnel through I believe (I think it's soft-soil landfill, since the ground has far less inherent rigidity).